Generally, many organic compounds have been known as substances that manifest photochromism and electrochromism. The term "photochromism" as used herein refers to a phenomenon that a substance, on exposure to light, emits color or changes color and, on release from the stimulus or exposure to other form of energy, regains the original state thereof and the term "electrochromism" refers to a phenomenon that a substance, when a voltage is applied thereto or a current is passed therethrough, changes color.
The aforementioned organic compounds manifesting photochromism and electrochromism [hereinafter referred to as "color-generating (or color-changing) organic compounds"] are so deficient in thermal resistance and acidproofness that they succumb to degradation of quality after exposure to repeated cycles of alternate oxidation and reduction in the air and, when spread on a surface, they are liable to produce minute crystals and are unfit as coating materials which are expected to produce smooth coatings.